PINEHURST, N.C. – Up by a half-dozen shots and exhibiting nothing but all the confidence in the golf world, Martin Kaymer is not about to chalk up his second career major just yet.

“It’s not a done deal,” Kaymer insisted after capping a historical-opening 36 holes and grabbing an imposing U.S. Open lead Friday courtesy of mind-numbing, back-to-back 5-under-par 65s in the first two rounds.

Brendon Todd, after a solid 67, is alone in second six shots back. Kevin Na (69) and Brandt Snedeker (68) are seven back. In a group eight back are Dustin Johnson (69) and Henrik Stenson (69). Rory McIlroy (68) and Jordan Spieth (70) are nine back as there are only 13 players under par.

Kaymer, the 2014 Players Championship winner, is the only one to break 67 this week and equaled the largest lead in U.S. Open history after 36 holes, matching the marks set by Tiger Woods in 2000 and Rory McIlroy in 2011.

Yet he sounds like a guy who is tied for the lead.

“You don’t approach Saturday and Sunday in a relaxed way,” added Kaymer, a former world No. 1 and the winner of the 2010 PGA Championship. “There’s never a time where you can relax. Unless it’s Sunday and you’re raising the trophy, then you can relax. Until then, you’ve got to keep playing.”

That’s what world No. 1 Adam Scott is going to do. Earlier this year Scott blew a 7-shot lead after 36 holes at the Arnold Palmer Invitational and knows full well they don’t crown the champion Friday night.

“If he does [this] for two more days, then we’re all playing for second spot,” said Scott, who is even par and 10 shots back after a 67. “But we all know that U.S. Opens get very difficult and if I can just somehow put together two really good rounds, maybe slowly but surely I’ll creep my way up towards Martin.

“I think if I drew up my perfect plan right now, over the next 27 holes you would like to narrow the gap to, you know, less than half of what the lead is. Anything could happen over nine holes at a U.S. Open.”

Kaymer has executed his game plan perfectly through two rounds, making few mistakes, aiming aggressively at conservative targets and putting beautifully to dismantle rugged No. 2.

With a flawless 65 in the second round on grounds softened by 6/10ths of an inch of overnight rain, Kaymer’s 130 total through two rounds broke the previous U.S. Open record of 131 set by Rory McIlroy in 2011.

He is the only player to begin a major championship with two 65s. He also became just the sixth player to reach double digits under par in a U.S. Open, joining Gil Morgan (1992), Tiger Woods (2000), Jim Furyk (2003), Ricky Barnes (2009) and McIlroy (2011).

“Martin seems to be playing a different golf course … 10-under is incredible,” said Brooks Koepka, who is eight shots behind.

But Koepka nor anyone else is waving a white towel. Precedent has been set for big comebacks (or collapses, if you will) in the U.S. Open.

Arnold Palmer had a 7-shot lead with nine to play in 1966 at the Olympic Club but eventually lost in a playoff the next day to Billy Casper.

In 1975 at Medinah, Lou Graham won after trailing Tom Watson by 11 strokes at the midway point. And in 1992, Morgan led by seven shots early in the third round and was not a factor as Tom Kite won at Pebble Beach.

“You never know what will happen in a U.S. Open,” said Phil Mickelson, who after a 73 is 13 shots back. “We have always had crazy things happen. There’s a lot of guys right there ready to pounce if he slips up.”

One would be Bradley who has fired consecutive 69s.

“He’s got a big lead, but that doesn’t really change anything I’m going to do. I’m still going to go out and if I can shoot all four rounds in the 60s, man, that would be pretty tough because I expect the course to get harder and harder as the week goes on,” Bradley said. “There’s no place to force anything. It’s just similar to Augusta [National] in that there’s a double [bogey] on every hole, if you’re not careful. So stick to the game plan.

“ … You need to go out there tomorrow and make a bunch of pars and you never know what’s going to happen.”

But Steve Stricker, who is 1-over after a 71, said the rest of the field needs help from Kaymer if there is to be some drama.

“If he plays even on the weekend, he wins,” Stricker said. “Because I don’t see anyone getting to 10-under par [by the end of the tournament].”